Briefly, the banding material used in the heat sealing of closures to containers is supplied in the form of a substantially continuous roll of tubular material with the walls of the tubular material flattened and fed off the roll as a semi-continuous ribbon having opposed creased edges. The ribbon of banding material is fed from the roll to equipment which opens it and thereafter delivers the opened banding material to a station on a production line where pieces are cut to a suitable size and applied over the lids of containers as they move past the station. Once in place, an application of heat to the banding material causes it to shrink tightly over the lid, providing a protective seal which must be broken in order to remove the lid from the container. As is well recognized, these seals provide a measure of protection to the ultimate purchaser who can readily tell from the condition of the heat sealed band whether someone has opened the container between the time it is sealed and the time of purchase.
The use of tetrahedrally-shaped mandrels having faces which are isosceles triangles to open the band of heat sealable material is known in the art. The banding material is drawn over the mandrel with the common corners of two of the isosceles triangular faces being in alignment with and in contact with the inner surfaces of the opposed creases of the material. As the banding material is drawn relatively lengthwise of the mandrel it is wedged open by these faces. The corners formed at the common base of the other two triangular faces impart creases which are offset by 90.degree. with respect to the original creases. Opening mandrels which perform this function are known per se and are disclosed in U.S. Pat. No. 4,148,171. The imparting of these additional creases acts to open the band and to naturally hold it in the open position so that it can be quickly and reliably fitted over the container lid during the application and sealing steps of the banding process.